Allow unwrap() in tests when clippy::unwrap_used is denied (#11616)

## Problem

The proxy denies using `unwrap()`s in regular code, but we want to use
it in test code
and so have to allow it for each test block.

## Summary of changes

Set `allow-unwrap-in-tests = true` in clippy.toml and remove all
exceptions.

clippy.toml

@@ -12,3 +12,5 @@ disallowed-macros = [
     # cannot disallow this, because clippy finds used from tokio macros
     #"tokio::pin",
 ]
+
+allow-unwrap-in-tests = true